Nestling Development of Jackdaws Corvus Monedula in Agricultural Landscape
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Intern. Stud. Sparrows 2015, 39: 4-23 DOI: 10.1515/isspar-2015-0030 Piotr KAMIŃSKI1, 2, Leszek JERZAK3, Joerg BOEHNER4 1 Nicolaus Copernicus University in Toruń, Collegium Medicum in Bydgoszcz, Faculty of Medicine, Department of Ecol- ogy and Environmental Protection, M. Skłodowska-Curie St. 9, PL 85-094 Bydgoszcz, Poland, phone (00 48 52) 585 38 05, fax (00 48 52) 585 38 07, e-mail: [email protected], [email protected] 2 University of Zielona Góra, Faculty of Biological Sciences, Department of Biotechnology, Prof. Szafran St. 1, PL 65-516 Zielona Góra, Poland, phone (00 48 68) 328 68 72, fax (00 48 68) 328 73 23, e-mail: [email protected] 3 University of Zielona Góra, Faculty of Biological Sciences, Department of Nature Protection, Prof. Szafran St. 1, PL 65-516 Zielona Góra, Poland, phone: (00 48 68) 328 78 72, (00 48 68) 328 24 85, fax (00 48 68) 328 73 23, e-mail: [email protected], [email protected] NESTLING DEVELOPMENT OF JACKDAWS CORVUS MONEDULA IN AGRICULTURAL LANDSCAPE ABSTRACT A Jackdaw colony of over 200 nests, built in cavities of old willow trees along 3 km of a small road running through meadows next to the river Narew in an agricultural landscape (15 km southwest of Białystok, NE Poland), was studied to determine nest locations and construction, onset of egg laying, incubation period, egg parameters, clutch size and hatching success, nestling growth and mortality, breeding success as well as predation . The onset of laying and clutch size were correlated with ambient temperature and precipitation (p < 0 .001) . Hatching success was also determined by these environmental factors as well as by the degree of predation (p < 0,001) . There was a statistically significant correlation between clutch size and hatching success (p < 0 .001) as well as fledging success (p < 0 .001) . Nestlings hatching first or second grew faster, reached a higher body weight, and had a lower mortality rate than those hatching last or second to last . There was also a statistically significant correlation between nestling survival and clutch size as well as ambient temperature (p < 0 .001 each) . Nestling mortality caused by predators, i . e . mainly by martens Martes foina and domestic cats Felis domestica, was high in periods of intensive burning of the meadows surrounding the Jackdaw colony . However, mortality rate of the youngest nestlings was almost 100% lower in periods of high predation compared to times of low predatory activity . Several groups of insects constituted a high amount of nestling food, e . g . 60% of all Orthoptera occurring in the meadows next to the breeding colony . In that area the total dry body mass of phytophagous invertebrates amounted to 1 .4-2 .0 g per m2, of which 0 .3 g were fed to the nestlings . The percentage of zoophagous invertebrates deliv- ered to the offspring was high with about 30-35% . From an economical point of view, Jackdaws during the breeding season are advantageous in an agricultural landscape because they reduce pest insects significantly while consuming only an insignificant amount of all seeds applied . Vol . 39 / 2015 5 Key words: Jackdaw, Corvus monedula, breeding ecology, hatching success, breeding success, nestling mortality, predation INTRODUCTION Corvids clutch size is determined by environmental factors (Haartman 1967) . Several studies revealed that a great majority of young birds reach independence late, hatch from a rather big egg and depend on the parents as nestlings (Ricklefs 1968, 1969, 1973, Blem 1975, O’Connor 1978a, b, Dunn 1980) . It has even been demonstrated that varia- tion in first clutches and in brood size is genetically determined by 40% (Van Noordwijk et al . 1981a, b, c) and variation in egg size can be as high a 60-80% (Ojanen et al . 1979, Van Noordwijk et al . 1980) . In the higher latitudes breeding starts later and nestling development is shorter . However, in regions far north many species which reproduce late in the course of the year start breeding at a lower temperature and phenologically earlier, which is an advantageous adaptation (Haartman 1963, Danilov 1967, Hussell 1972, Slagsvold 1975a, b, Vogel 1990, Kamiński 1991, Strebel 1991) . Of course the limiting factor for an early onset of breeding is a sufficient food supply for females to produce eggs (Perrins 1970, Schmidt 1988) . Supplementary food significantly increased fledging success in less than half of experimental studies in Jackdaw colonies . The key to this problem is probably the species’ breeding strategy; supplementary food signifi- cantly increased fledging success in species exhibiting brood-reduction strategies but not in species which directly adjusted their clutch size (Soler & Soler 1996) . Jacobs et al . (2013) reported that food caching is a paramount model for studying relations between cognition, brain organisation and ecology in crows and Jackdaws . In contrast, behaviour towards inedible objects is poorly examined and understood . Migration and wintering of Jackdaws have already been investigated (Grodziński 1971) but data on the reproductive ecology of populations nesting in naturally flooded meadows and farmland are still missing . As far as other corvid species are concerned, the spatial structure and the mechanisms of self-regulation of Rook Corvus frugilegus populations (Józefik 1976) as well as changes in distribution and abundance of the Common Raven Corvus corax in Central Europe have been studied (Dobrowolski et al . 1962) . On the other hand, Verhulst and Salomons (2004) stated that social dominance is intuitively assumed to be associated with higher fitness, because social dominance implies better access to resources . Jolles et al . (2013) analyzed heterogeneous structure in mixed-species corvid flocks in flight . Schwab et al . (2008) suggested that affiliated social relations may facilitate information transfer between Jackdaw individuals . de Kort et al . (2006) explored the extent and pattern of food sharing in a group of juvenile Jackdaws . The aim of the present study was to determine important ecological parameters of the breeding ecology of Jackdaws nesting in natural tree cavities and to investigate the dependence of these parameters on environmental factors . 6 International Studies On Sparrows STUDY AREA AND METHODS From 1981 to 1994, a population of Jackdaws nesting in naturally flooded meadows and farmland near the river Narew, about 15 km southwest of the city of Białystok (north-eastern Poland), was studied . 200 nests were investigated, all of which were located in natural cavities of old willow trees, mainly Sallow willow Salix caprea, along an agricultural road crossing flooded meadows of the river Narew . A total of 490 nests were checked daily, and the date of the first egg laid, time until clutches were complete, period of incubation, size and weight of eggs, hatching success, mortality of nestlings and breeding success were determined . The following parameters were estimated: hatching success (percentage of eggs that hatched per nest for each clutch size separately), breeding success (percentage of hatched nestlings that fledged per nest for each clutch size separately), and nestling mortality (percentage of hatched nestlings that died at successive days of life) . In addition, the location of the nest site was recorded and observations on nest building were made . Eggs were weighted with a spring scale (Pesola Co . Ltd .) to the nearest 0 .1 g and measured with a cruising rod . Eggs for the biochemical analysis were dried at 65oC for 48 h and grinded in an electri- cal mill . Water content was determined from the egg weight before and after drying . Protein content was determined with the Kjeldahl method and fat content with the gravimetric method (A sample of about 1 g was extracted with a mixture of chloroform and methanol (2:1) at 60oC and then with a cold mixture of chloroform and ether (1:1) . After evaporation at 50oC and extrusion of air, the samples were dried to dry weight . The resulting mass difference equals the extracted amount of fat .) . The energy value was determined with a KL-5 closed calorimetric system after Berthelot . RESULTS Nest site and construction In the study area, Jackdaws bred colonially and located their nests in natural, decayed cavities of Willow trees, growing along an agricultural road for about 3 km . Most often nest were built in a height of 3-7 m and only rarely as low as 1-1 .5 m or above 15 m . Cavity depth and entrance width varied, but nests were mainly built in cavities 60-80 cm deep and 30-40 cm wide . However, some nests were found in very short (depth 2-5 cm and entrance width 15-20 cm) as well as in very deep (more than 3 m) and varying holes, with several crooked passages within the tree, a couple of entrances and entrance diameters of 8-50 cm were recorded . Nests were mainly constructed of thin (0 .5 cm) twigs and were bolstered with hair of various types, e .g . from horses, and scraps of paper . Nest in short cavities contained a lot of nesting material, which was almost missing in deep cavities where egg and young simply lay on decaying wood . Vol . 39 / 2015 7 Egg laying and incubation The beginning of egg-laying differed between years, with a maximum range of 21 days . The earliest date recorded was April 8 (1984), the latest April 28 (1986) . Most often clutches were initiated around mid-April . The start of egg-laying was determined by a mean daily ambient temperature of about 100 C as well as by air humidity and pre- cipitation (Tab . I, Figs . 1-3) . Clutch size varied between 2 and 6 eggs which were laid at an interval of 1-2 and rarely 3-5 days . Mean clutch size was 4 .9±0 .3 eggs .